Drying apparatus with feed and humidity control

ABSTRACT

An improved dryer for bulk material of the type employing a feed apron, a pin elevator and an endless, foraminous belt moved through a series of air drying zones, the improvement comprising (A) a humidity transducer in the air exhaust stack arranged to regulate flow of steam to a sparger under the belt in a zone and (B) a power level transducer attached to the pin elevator drive motor, a temperature transducer located under the belt in the final zone, each transducer connected through a separate controller to a booster relay arranged to select the lower of the two control signals and apply this to regulate feed apron drive motor speed.

United States Patent 1191 Driscoll et al.

[11] 3,783,527 Jan. 8, 1974 DRYING APPARATUS WITH FEED AND HUMIDITYCONTROL [73] Assignee: E.I. du Pont de Nemours and Company, Wilmington,Del.

22 Filed: Dec. 13, 1972 211 App]. No.: 314,603

[52] US. Cl 34/56, 34/54, 34/52,

- 34/44 [51] Int. Cl. F26d 13/12, F26b 21/08 [58] Field of Search..34/56, 52, 54, 50, 34/44, 45, 51

[56] References Cited UNITED STATES PATENTS 3,186,102 6/1965 Brociner eta1. 34/56 X 3,259,995 7/1966 Powischill 34/54 X 3,396,476 7/1 968 Eves34/52 X 3,599,343 8/1971 Nielson 34/52 T0 CUTTER STA 1011s COMPUTINGRELAY CUTTERS CONTROLLER TO BELT MOTOR Arnold ..l 3.4/51 x FOREIGNPATENTS OR APPLICATIONS 480,355 1 1952 Canada .l .L ..34 44 PrimaryExaminer--William F. ODea Assistant Examiner-Paul DevinskyAttorney-Howard P. West, Jr.

[57] ABSTRACT An improved dryer for bulk material of the type employinga feed apron, a pin elevator and an endless,

foraminous belt moved through a series of air drying zones, theimprovement comprising (A) a humidity transducer in the air exhauststack arranged to regulate flow of steam to a sparger under the belt ina zone and (B) a power level transducer attached to the pin elevatordrive motor, a temperature transducer located under the belt in thefinal zone, each transducer connected through a separate controller to abooster relay arranged to select the lower of the. two control signalsand apply this to regulate feed apron drive motor speed,

2 Claims, 1' Drawing Figure 111011 515114 SUPPLY DRYING APPARATUS WITHFEED AND HUMIDITY CONTROL BACKGROUND OF THE INVENTION This inventionconcerns apparatus for improved drying of loose bulky material such astextile staple fibers in bulk. More specifically, it relates toauxiliary control apparatus appended to a continuous dryer which employsan enclosed endless foraminous belt and circulating air.

Uniform rate of drying and final level of moisture content are importantto product quality. Color, dyeability and openness of synthetic fiberstaple products are often adversely affected by variable or poorlyregulated drying conditions.

A significant improvement in controlling dryers of this type has beenrealized by the apparatus of Powischill in U.S. Pat. No. 3,259,995.However, further improvement was required for certain drying systemssuch as, for example, a system where the dryer is supplied from a hopperthat has an intermittent input. A case in point is a dryer of the typefor textile staple wherein the feed hopper is supplied from tow cutters,one or more of which must be interrupted for splices, knife change, etc.In these cases, the hopper fill level may vary sharply and the rate offeeding of staple to the dryer as well as dryer conditions requirespecial regulation.

SUMMARY OF THE INVENTION This invention provides apparatus attached toan enclosed endless belt dryer chamber that is supplied with bulkmaterial in a hopper by a feed apron in the bottom of the hopper and apin elevator extending from the apron to deposit material on the belt.Both the apron and the pin elevator are independently driven by variablespeed motors. Improved regulation of the extent of drying is provided bythe novel auxiliary control apparatuses of this invention. Thesecomprise in combination wet and dry bulb temperature transducers in theexhaust duct. These transducers are connected to a computing relay. Theresulting difference Signal is fed to a controller arranged'to regulatethe flow of steam to a steam sparger located under the belt at aposition along the belt which is near the latter stages of drying. Thebelt enclosure is separated into three zones along its length bytransverse partitions. Circulating fans bring air in from the roomoutside the enclosure and pass it over control conditioning elements,then through the belt from above to below and finally exhaust through aduct.

In addition to sparger control effects, further improvement is providedby a temperature transducer located under the belt in the last zone ofdrying. This transducer is connected to a first of two companioncontrollers. A power level transducer is attached to the motor of thepin elevator and the output signal of this transducer is connected tothe second controller. The outputs of these controllers are connected toa booster relay which selects the lower signal. The output of this relayis connected to the speed controller of feed apron motor of the supplyhopper. Thus, the speed of the feed apron is regulated in response toeither pin elevator power drop below set point or below belt temperaturedropping too low.

These improvements may be used in conjunction with or as a replacementfor one or more of the known arrangements, e.g., those of Powischill.These known methods include: (A) control of the dryer belt speed; (B)control of fan motors; (C) control of an exhaust damper; (D) adjustmentof a unit to humidify incoming air; and (E) regulation of steam supplyto heaters employed in conditioning the air used for drying, all inresponse to the below belt temperature measurement.

BRIEF DESCRIPTION OF THE DRAWING The Drawing is a schematic plan view ofan endless belt enclosed dryer and acircuit diagram showing the novelcontrol features of this invention attached thereto.

DESCRIPTION OF THE PREFERRED EMBODIMENT An understanding of theapparatus of this invention can best be achieved by reference to theattached drawing. The preferred apparatus is described in connectionwith the drying of synthetic textile staple fibers in bulk which arereceived from textile tow cutters, not shown, and which after drying aretransported to staple balers also not shown. The novelty of theinvention lies in the control apparatus appended to a substantiallyconventional dryer.

The dryer as shown in the drawing comprises an endless foraminous belt10 extending around drive sprockets l2, l4. Sprocket 14 is driventhrough chain 16 by gear motor assembly 18. Optionally, motor 18 has aspeed control component 20 which is responsive to a thermocouple 22located underneath the belt 10 near the exit end of the belt. The upperhorizontal leg of belt 10 extends from the input end underneath a shoe24 which is designed to push the material being dried down onto thebelt. In some cases, this shoe is provided with a steam supply andperforations for applying steam to the incoming bulk material. The beltextends into a drying enclosure 26 which is divided into three dryingzones 27, 28, 29. Each zone is substantially the same size and has aconfiguration essentially the same as that shown by Powischill in U.S.Pat. No. 3,259,995.

rator 42 from which it drops into feed hopper 44. The

bottom of hopper 44 comprises a feed apron 46 which is driven throughchain 48 by variable speed motor 50, such as a Reeves drive with Airtrolunit attached. At the exit end of apron 46, there is provided a pinelevator arrangement 52 which is driven through chain 54 by variablespeed motor 56. A withdrawing roll 58 and a scrapping bar 60 arearranged as shown and driven through chain 64 by variable speed motor62. Two photoelectric staple level detectors 66, 68 are located in thesides of hopper 44 at locations as shown. The upper detector 66 isarranged to send a signal to the staple cutters when the level of stapleto be dried becomes excessive within hopper 44. Detector 68, on theother hand, sends signals to stop the belt 'motor 18 when the levelpasses below a critical limit and restarts motor 18 when the level risesagain above detector 68. Time delay circuits are provided in connectionwith the outputs of these detectors to avoid reaction to very transientover or under supply.

The novel control features of this invention comprise I first a wet anddry bulb temperature transducer 70 located within the stack 40.Transducer 70 has attached thereto a conventional fluid-to-airtransducer so that pneumatic signals are transmitted over lines 71, 71to a computing relay 72.

The dry and wet bulb temperature signals are algebraically combined inthe computing relay 72 to provide an output signal to controller 74proportional to the difference between the dry bulb and wet bulbtemperatures and consequently related to the relative humidity of theair in stack 40. Thus, pneumatic controller 74 (typically a Moore SyncroStation) provides signals for adjusting valve 76 to control the flow ofsteam through pipe 78 to sparger 80 and out through nozzles 81. In thisway, the quantity of steam forced upward through fan 31 and down throughthe sample being dried is based on the relative humidity of the airexhausting from the dryer. This forms the first part of the addedcontrol system.

The second part of the novel control system comprises a duel inputselective control in which a power level transducer 84 (Halltiplyer WT31K5) is con-.

nected through cable 85 to pin elevator motor 56. The signal fromtransducer 84 is passed to a first controller 86 over cable 87 through aconventional voltage-to-air pressure transducer not shown. The output ofpneumatic controller 86, which in the preferred embodiment is MooreSyncro Station, is passed first over line 89, to a Mercoid switch 90 andthen to the start-stop mechanism of motor 50 over line 93. A secondoutput from controller 86 is transmitted over line 91 to a first inputterminal of a booster relay 94 (Moore Products C0., Model 61). Atemperature transducer 96 is located under the dryer belt near the exitend of the drying stages and arranged to provide a signal over line 97to another (Moore Syncro Station) controller 98-. Output from controller98 is transmitted over line 99 to a second input terminal of boosterrelay 94. The output signal from relay 94 is connected over lines 101and 103, respectively, to the speed control unit (Airtrol unit) of feedapron drive motor 50. This signal also goes to recorder 104 (RustrackRecorder)and thence to a system of readout devices located at the lowcutter stations. Relay 94 is designed to select the lower of the twoinput control signals and transmit its output control signal based onthis selection.

This invention provides two important means for the regulation of themoisture content in materials being dried on an endless belt. Therelative humidity of the air exhausted through stack 40 is employed toregulate the opening of the valve which controls the amount of steamblown down through the material being dried, thus evening out humidityin the drying air and therefore, reducing potential wet spots in thematerial. In addition, one signal based on the amount of power beingdrawn by the pin elevator motor, which is related to the drying loadlevel being imposed on the dryer, is used to provide one possible signalfor regulating the rate of supply of material by adjusting the speed ofthe feed apron 46. An alternate signal is provided by a readout of thetemperature of the air underneath the dryer belt near the dry end of thedrying zones. These two signals are employed by respective controllers86, 98 to provide two signals to a booster relay which selects the lowerof the two signals (power level or underbed temperature) to provide theregulating signal for the speed of apron motor 50.

The utility of this invention lies in the attainment of more uniformproduct which is desirable. In actual tests, a comparison was madebetween operation of a I trol system of this invention was put intooperation on the same dryer, the number of moisture stops per day wasreduced to a very low level of only two and this had the corollaryeffect of increasing possible dryer throughput by about 4 percent.Furthermore, it was found that manual control was able to maintain adryer rate variation at no better than i 20 lb. per min. whereas the newsystem controlled the rate of variation in dryer throughput to a levelof i 10 lb. per min. This obviously provides improved fiber heattreatment uniformity and consequent improvement in dyeability uniformityand uniformity in color of the production.

Although this invention has been described in terms of the presentpreferred embodiment wherein synthetic textile staple is dried, thenovel structure and function of this invention is applicable to thedrying of other bulk materials which may be fed by means of a feed apronand pin elevator onto an endless forarninous belt and dried withcirculating air. In addition, the invention is described in terms ofpneumatic controller devices. Obviously electronic controllers could besubstituted and other variations would be apparent to those skilled inthe art without departing from the spirit of the present invention. 7

What is claimed is: g

1. In an apparatus for continuously drying material including an endlessbelt dryer chamber supplied with material by a pin elevator driven by amotor and a feed apron driven by a variable speed motor the improvementcomprising: a power level transducer connected to the pin elevator motorfor detecting the power consumed by the pin elevator motor and forgenerating first signals proportional to the power consumed by the pinelevator motor; a temperature transducer located in said dryer chamberfor detecting the temperature therein and for generating second signalsproportional to the temperature detected; means for comparing said firstand second signals and for selecting the lower of said signals; and acontroller connected to said feed apron motor for regulating the speedof said feed apron motor, said controller being actuated by the lower ofsaid first and second signals.

2. The apparatus as defined in claim 1, said dryer chamber having anexhaust duct connected thereto and a steam sparger located therein'foradmitting steam into said chamber and further including means fordetecting relative humidity in said exhaust stack and generating thirdsignals proportional thereto; a controller connected to said steamsparger for regulating the steam flow therethrough, said controllerbeing actuated by said third signals.

1. In an apparatus for continuously drying material including an endlessbelt dryer chamber supplied with material by a pin elevator driven by amotor and a feed apron driven by a variable speed motor the improvementcomprising: a power level transducer connected to the pin elevator motorfor detecting the power consumed by the pin elevator motor and forgenerating first signals proportional to the power consumed by the pinelevator motor; a temperature transducer located in said dryer chamberfor detecting the temperature therein and for generating second signalsproportional to the temperature detected; means for comparing said firstand second signals and for selecting the lower of said signals; and acontroller connected to said feed apron motor for regulating the speedof said feed apron motor, said controller being actuated by the lower ofsaid first and second signals.
 2. The apparatus as defined in claim 1,said dryer chamber having an exhaust duct connected thereto and a steamsparger located therein for admitting steam into said chamber andfurther including means for detecting relative humidity in said exhauststack and generating third signals proportional thereto; a controllerconnected to said steam sparger for regulating the steam flowtherethrough, said controller being actuated by said third signals.